1. Field of the Invention
The present invention relates to a receiver for receiving multiplexed data and multiplexed facsimile data broadcast in addition to sound multiplex broadcasting and teletext broadcasting, which have been so far broadcast multiplexed to the television broadcasting.
2. Description of the Related Art
In the so-called information-oriented era as we are today, attention is focused on data broadcasting for broadcasting digital data and also on facsimile broadcasting for broadcasting image data in addition to sound or picture, as broadcast so far.
The broadcasting as described above can be executed via dedicated media such as a broadcasting satellite. However, in order to effectively utilize radio wave resources, technical development work is positively concentrated on multiplex broadcasting which utilizes the radio wave of audio broadcasting or television broadcasting already in existence.
Like multiplex broadcasting, there are stereo broadcasting, sound multiplex broadcasting, teletext broadcasting, facsimile broadcasting and data broadcasting that utilize a broadcasting wave.
Among these type s of multiplex broadcasting, stereo broadcasting based on FM broadcasting waves and television broadcasting waves is now executed in practical application in Japan. Also, sound multiplex broadcasting and teletext broadcasting based on television broadcasting waves are also found in practical application. Facsimile broadcasting based on FM broadcasting waves is in practical application in the U.S.A., while broadcasting based on television broadcasting waves is under study in Japan. Data broadcasting based on FM broadcasting waves is now being practiced in Japan, and broadcasting based on television broadcasting waves is considered a subject for future study and development.
An example of multiplex broadcasting is given in particular using a television wave taken on the radio wave of NTSC color television broadcasting , which is now adopted in Japan and U.S.A.
As shown in FIG. 1, the radio wave of NTSC color television broadcasting comprises a video carrier with a bandwidth of 5.5 MHz (i.e., 4.25 MHz above the center frequency of the video carrier and 1.25 MHz below) and an audio carrier with a bandwidth of 0.5 MHz having the center frequency at 4.5 MHz above the video carrier (i.e., .+-.0.25 MHz). Thus, the total bandwidth is 6 MHz.
Among the types of multiplex broadcasting described above, in teletext broadcasting based on television broadcasting waves, data is transmitted in multiplex utilizing the vertical blanking interval in the television video signal contained in the video carrier. In FM stereo broadcasting, FM data broadcasting, FM facsimile broadcasting, television stereo broadcasting, television audio multiplex broadcasting and television facsimile broadcasting, programs are broadcast via sub-carrier in the audio band.
Following is a description of multiplex broadcasting based on sub-carrier according to a report of the Facsimile Broadcasting Committee of the Telecommunication Technical Council on television audio multiplex broadcasting and television facsimile broadcasting (Feb. 16, 1989). FIG. 2 shows a modulation spectrum according to such television multiplexed facsimile broadcasting system. In this figure, the audio carrier is represented on the abscissa axis (having horizontal scanning frequency; i.e., fH=525 lines.times.59.94, Hz/2=15.73425 KHz as a unit), and the deviation to the main carrier (having KHz as a unit) is represented on the ordinate axis.
In this multiplex broadcasting modulation spectrum, the center frequency of the main audio carrier is 0 fH, and the center frequency of the audio sub-carrier for sub audio, used for stereo and dual sound, is 2 fH. In this case, the deviation of the stereo sound is considered to be .+-.20 KHz, and the deviation of the dual sound is .+-.15 KHz. Also, the center frequency of the sub-carrier for the control signal to control the sub audio is at 3.5 fH.
The center frequency of the sub-carrier for analog facsimile is at 6 fH, and frequency range is from 4 fH to 8 fH. Because analog facsimile may impair sound multiplex broadcasting, it is not possible to multiplex the facsimile signal during sound multiplex broadcasting. For this reason, it is now attempted to have audio multiplex and analog facsimile at the same time by deleting the frequency range from 4 fH to 5 fH.
In contrast to analog facsimile, the center frequency of the sub-carrier for digital facsimile is at 4.5 fH, in view of impairment to sound multiplex broadcasting, and the operating frequency range is 1 fH (i.e., from 4 fH to 5 fH), and the frequency deviation of the main carrier is .+-.2 KHz. For the modulation system, Quadrature Phase Shift Keying (Quadrature PSK) is adopted.
FIG. 3 represents a block diagram of a conventional type television receiver, which receives TV stereo sound, TV dual sound and TV teletext data in addition to TV pictures. This television receiver comprises a TV tuner portion, a TV video processor portion and a TV audio processor portion. The TV tuner portion 2 is connected to a TV antenna 1. The TV video processor portion comprises a video detector 3 connected to the TV tuner 2, a signal separator 4 connected to the video detector 3, a video amplifier 5 and a teletext data demodulator 7, each connected to the signal separator 4, and a TV picture display unit 6, such as a cathode ray tube, which is switched over to the video amplifier 5 or to the teletext data demodulator 7.
The TV audio processor portion comprises a TV audio detector 8 connected to the TV tuner 2, a TV main/sub audio separator 9 connected to the TV audio detector 8, a TV sub audio demodulator 10 connected to the TV main/sub audio separator 9, a TV stereo matrix circuit 11 connected to the TV main/sub audio separator 9 and to the TV sub audio demodulator 10, a TV dual sound circuit 12 connected to the TV sub audio demodulator 10, and speakers 13 connected to the TV stereo matrix circuit 11 and to the TV dual sound circuit 12.
When a TV signal is received by the TV antenna 1, the video signal and audio signal are tuned and selected by the TV tuner 2. The video signal thus selected is detected by the video detector 3 and is further separated into a synchronization signal and a video signal at the signal separator 4. The video signal is displayed on the TV picture display unit 6 via the video amplifier 5. The teletext data multiplexed on the synchronization signal is picked up from the separated synchronization signal and is demodulated at the teletext data demodulator 7. Further, it is converted to the video signal and is displayed on the TV picture display unit 6.
On the other hand, the TV audio signal is also detected by the TV audio detector 8 and is separated into a main audio signal and a sub audio signal at the TV main/sub audio separator 9. In case the sub audio is a TV stereo sound, the stereo sound is picked up from the main audio signal and the sub audio signal demodulated at the TV sub audio demodulator 10 by the TV stereo matrix circuit 11. In case the demodulated sub audio is a TV dual sound, the sub audio signal demodulated at the TV sub audio demodulator 10 is picked up via the TV dual sound circuit 12. These audio signals are then converted to sound via the speakers 13.
FIG. 4 represents a block diagram of a conventional type television receiver for receiving TV multiplexed facsimile data signals in addition to stereo sound, dual sound and teletext data signals, together with pictures. This television receiver comprises a TV tuner, a TV video processor, and a TV audio/multiplexed-facsimile-data processor.
Among these component elements, the arrangement and the operation of the TV tuner and the TV video processor, as well as the arrangement and the operation for processing TV stereo sound and TV dual sound, are the same as the arrangement and the operation of the television receiver shown in FIG. 3; therefore, a detailed description is not repeated here. In addition, a first band-pass filter 14, allowing a first sub-carrier of 4.5 fH to pass, is connected to the TV audio detector 8. A TV multiplexed facsimile data demodulator 15 is connected to the first band-pass filter 14, and a TV multiplexed facsimile data printer 16 is connected to the TV multiplexed facsimile data demodulator 15.
The first sub-carrier of 4.5 fH multiplexed on the TV audio signal is selected by the first band-pass filter 14 as it passes through. The first sub-carrier selected by the first band-pass filter 14 is sent to the TV multiplexed facsimile data demodulator 15. The TV multiplexed facsimile data sent from the first sub-carrier is demodulated at the TV multiplexed facsimile data demodulator 15 and the TV multiplexed facsimile data thus demodulated is printed by the TV multiplexed facsimile printer 16.
FIG. 5 shows a block diagram of a conventional type receiver for receiving FM multiplexed facsimile data together with stereo audio of FM broadcasting. The receiver comprises an FM tuner, and an FM audio/multiplexed-facsimile-data processor.
The FM tuner comprises an FM tuner 18 connected to an FM antenna 17. The FM audio/multiplexed-facsimile-data processor comprises an FM detector 19 connected to the FM tuner 18, an FM main/sub audio separator 20 connected to the FM detector 19, an FM sub audio demodulator 21 connected to the FM main/sub audio separator 20, an FM stereo matrix circuit 22 connected to the FM main/sub audio separator 20 and to the FM sub audio demodulator 21, and the speakers 13 connected to the FM stereo matrix circuit 22. Further, a third band-pass filter 23 allowing sub-carrier for FM facsimile data to pass is connected to the FM detector 19. An FM multiplexed facsimile data demodulator 24 is connected to the third band-pass filter 23, and an FM multiplexed facsimile data printer 25 is connected to the FM multiplexed facsimile data demodulator 24.
In this receiver, the FM broadcasting signal received by the FM antenna 17 is tuned and selected by the FM tuner 18. The audio signal thus tuned and selected is detected by the FM detector 19 and is separated into a main audio signal and a sub audio signal at the FM main/sub audio separator 20. From the main audio signal and the sub audio signal, the stereo audio is picked up by the FM stereo matrix circuit 22, and these audio signals are converted to sound by the speakers 13.
The sub-carrier for the FM facsimile data multiplexed on the FM audio signal is selected by the third band-pass filter 23 as it passes through. The sub-carrier for FM facsimile data selected by the third band-pass filter 23 is sent to the FM multiplexed facsimile data demodulator 24. The FM multiplexed facsimile data is demodulated from the sub-carrier thus sent at the FM multiplexed facsimile data demodulator 24, and the demodulated facsimile data is printed by the FM multiplexed facsimile printer 25.
FIG. 6 shows a block diagram of a conventional type receiver for receiving FM multiplexed data broadcast together with stereo sound of FM broadcasting. This receiver comprises an FM tuner and an FM audio/multiplexed-data processor.
Among these component elements, the arrangement and the operation of the FM tuner and the processing of FM stereo sound are the same as those of the receiver shown in FIG. 5, and a detailed description is not given here. In addition, a fourth band-pass filter 26 allowing the sub-carrier for FM data to pass is connected to the FM detector 19. An FM multiplexed data demodulator 27 is connected to the fourth band-pass filter 26, and an FM multiplexed data display unit 28 is connected to the FM multiplexed data demodulator 27.
The sub-carrier for FM data multiplexed on audio signal is selected by the fourth band-pass filter 26 as it passes through. The sub-carrier for FM data selected by the fourth band-pass filter 26 is sent to the FM multiplexed data demodulator 27. The FM multiplexed data is demodulated from the sub-carrier at the FM multiplexed data demodulator 27, and the demodulated FM multiplexed data is displayed on the FM multiplexed data display unit 28.
It is noted that data broadcast utilizing the FM broadcasting wave as described above is now being used in practical application, and that data broadcast utilizing the television broadcasting wave is under study for future application.
The center frequency of the sub-carrier in multiplexed facsimile broadcasting using the television wave, being scheduled for practical application, is at 4.5 fH. The operating frequency bandwidth is to be 1 fH (i.e., from 4 fH to 5 fH), the frequency deviation of the main carrier is to be .+-.2 KHz, and Quadrature Phase Shift Keying (Quadrature PSK) is to be adopted for demodulation.
In addition, it has also been attempted to have the center frequency of the sub-carrier at 7.5 fH. However, it is considered that the video signal may be impaired, although there is not much hindrance to audio multiplexed broadcasting. For this reason, only one program may be broadcast in multiplex broadcasting, which can be multiplexed in addition to stereo broadcasting and audio multiplex broadcasting, as practiced so far for multiplex broadcasting utilizing the sub audio of television, and it is not possible to multiplex two-channel facsimile broadcasting, two-channel data broadcasting or one-channel facsimile broadcasting and data broadcasting.
Also, there exists an analog facsimile system in which the center frequency of the sub-carrier is at 6 fH and the frequency bandwidth is set from 4 fH to 8 fH. However, this analog facsimile may impair sound multiplex broadcasting, and it is not possible to multiplex the facsimile signal during the audio multiplex broadcasting. For this reason, it has been attempted to use audio multiplexing and analog facsimile at the same time by deleting the frequency bandwidth from 4 fH to 5 fH, but this is not yet practically applied.
Because digital facsimile signals consist of binary data as in the case of digital data signals, the digital data signal can be handled in the same manner as the digital facsimile signal. Data broadcasting using a sub-carrier of 4.5 fH of digital facsimile broadcasting multiplexed on television audio bandwidth is described in "A Proposal to Broadcast a Data Broadcast by use of Multiple Broadcasting System," by Kouji Sasano (Broadcasting System, 31st Conference of Commercial Broadcasting Engineering, pp.22-23, Japan Commercial Broadcasting Federation, Nov. 9, 1994). The setting of the frequency deviation of data signal sub-carrier to .+-.2 KHz and .+-.3 KHz is shown in "A Report for the Addition of a Third Subcarrier in the TV Audio," by Kouji Sasano (ITE '94: ITE Annual Convention, pp.359-360, Institute of Television Engineers, Jul. 29, 1994).
In cases where the center frequency of the sub-carrier is set to 7.5 fH, it has been considered that the video signal may be impaired, while there is less impairment to sound multiplex broadcasting. The present inventors have performed various types of experiments on these problems and found that no impairment occurs to the video signal in cases where digital modulation is performed with a sub-carrier of center frequency 7.5 fH in a Quadrature Phase Shift Keying system with a frequency deviation of the main carrier of .+-.2 to 3 KHz. Based on this finding, in a prior application, Japanese Patent Application No. 6-122388, the present inventors proposed a television multiplex broadcasting system in which a sub-carrier of 7.5 fH is modulated by facsimile or data digital signal with Quadrature PSK system.
According to the above multiplex broadcasting system, it is possible to carry out two-channel multiplex broadcasting by simultaneously executing multiplex broadcasting using a sub-carrier of 4.5 fH. This is also described in "The Measurements of the Interference on the over all TV Signal from a Digital Signal and a Third Subcarrier in the Audio Portion of the TV Signal," by Kouji Sasano (Broadcasting System, 31st Conference of Commercial Broadcasting Engineering, pp.26-27, Japan Commercial Broadcasting Federation, Nov. 9, 1994).
In the television multiplexed digital broadcasting system, consideration is given to impairment to sound multiplex broadcasting and impairment to video signal, and the frequency deviation of the sub-carrier with center frequency at 7.5 fH is set to .+-.2 to 3 KHz. For this reason, no special problem occurs when a program of television digital multiplex broadcasting, which is a data program, is received by a television receiver fixed at a place where an electric field strength of a certain degree is assured. However, in the case of a mobile receiver, such as the receiver on an automobile, that is at a place where sufficient electric field strength is not assured and where it is not possible to have an electric field with stabilized strength, and thus, because bit error rate and page error rate caused by crashing of eye pattern increase, it is very difficult to receive the multiplexed data program, as described in "TV Audio MPX-Data-Broadcast and Mobile Reception," by Kouji Sasano and Akeshi Kondo (ITE Technical Report, Institute of Television Engineers, Aug. 24, 1995).
In view of the above facts, the present inventors have performed receiving experiments under various conditions of television multiplex broadcasting and found that no impairment occurs to sound multiplex broadcasting or video signal if the frequency deviation of the data multiplex sub-carrier with center frequency at 7.5 fH is within .+-.30 KHz, and that stabilized data reception can be assured even under conditions when it is not possible to receive multiplex data programs because sufficient electric field strength cannot be assured or electric field with stable strength cannot be maintained, as in the case of a mobile receiver such as one on an automobile.
Further, it was discovered that no problem occurs in cases where the frequency deviation is set to .+-.20 KHz, and even when it is extended to .+-.30 KHz there is no practical problem, although there may be some impairment.
The present inventors have performed various types of experiments on multiplex broadcasting utilizing sub audio of television and confirmed that no impairment occurs to video signal when multi-valued digital modulation, such as Quadrature PSK system with a frequency deviation of the main carrier of .+-.30 KHz, is performed to the sub-carrier, even in cases when a sub-carrier with a center frequency of 7.5 fH is used.